Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$15.64	5.347%	$16.4763	$16.48	$16.50	$16.50
Purchase #2	$149.87	8.216%	$162.1833	$162.18	$162.20	$162.20
Purchase #3	$38.30	5.102%	$40.2541	$40.25	$40.25	$40.30
Purchase #4	$120.74	6.519%	$128.611	$128.61	$128.60	$128.60
Purchase #5	$116.59	11.470%	$129.9629	$129.96	$129.95	$130.00
Purchase #6	$79.84	7.582%	$85.8935	$85.89	$85.90	$85.90
Purchase #7	$80.50	12.836%	$90.833	$90.83	$90.85	$90.80
7 purchase totals =	$601.48		$654.2141	$654.20	$654.25	$654.30